There are speaker apparatus from which sounds are output by transmitting vibration generated at an actuator to a diaphragm through a vibration transmitting member. For example, the actuator used in such a manner may be a piezoelectric actuator, an electrostrictive actuator or the like. A material having high vibration transmitting characteristics may be used as the vibration transmitting member, and the diaphragm may be formed from, for example, a resin material such as an acrylic material.
In a speaker apparatus as thus described, when vibration generated at the actuator is transmitted to the diaphragm through the vibration transmitting member, a compressional wave is instantaneously propagated in the direction in which the vibration is transmitted (vibration exciting direction). During the propagation of the compressional wave, a force attributable to the Poisson's ratio of the solid body (diaphragm) is generated in a direction orthogonal to the vibration exciting direction. When the force in the direction orthogonal to the vibration exciting direction is generated, the force causes the diaphragm to vibrate, and sound waves are generated throughout the diaphragm to output sounds.
Therefore, in a speaker apparatus utilizing a vibration transmitting member and a diaphragm as thus described, sound waves are generated at a level that is uniform in any part of the diaphragm, and uniform acoustic characteristics can be achieved throughout the diaphragm.
Speaker apparatus of the above-described type include a speaker having an actuator disposed on one side of a cylindrical diaphragm when viewed in the axial direction of the diaphragm and a vibration transmitting member disposed in contact with one end face of the diaphragm when viewed in the axial direction of the diaphragm. Thus, vibration is transmitted to the end face of the diaphragm in the axial direction thereof to output sounds from the diaphragm (see JP-A-2007-166027 (Patent Document 1)).
In the speaker apparatus disclosed in Patent Document 1, when vibration is transmitted to the vibration transmitting member, a compressional wave is instantaneously propagated in the axial direction of the diaphragm. A force attributable to the Poisson's ratio of the diaphragm is generated in a direction orthogonal to the axial direction of the diaphragm to cause vibration of the diaphragm. Thus, sound waves are generated throughout the diaphragm, and sounds are output.